The clandestine meeting of royalty, prime ministers and business chiefs is taking place in Britain for the first time since 1998, sparking fears of “violence and disturbance” by protesters.

The Bilderberg organisers, who include Tory Cabinet minister Ken Clarke, do not release a guest list but a roll-call of luminaries are expected to descend on a luxury Watford hotel from June 6, forcing police to step up security.

Hertfordshire police have refused to release the cost of security for the event, which has previously drawn anti-capitalist demonstrators in other locations around the world.

However, they are in talks with the Home Office about a grant for “unexpected or exceptional costs” that is only given out if it threatens the stability of the force’s policing budget. The final bill would have to total more than one per cent of the police force’s overall spend – or about £1.8 million – for the grant to be successful.

The invitation-only Bilderberg meetings are attended by around 140 members of the international elite.

Previous guests are thought to have included Henry Kissinger, David Rockefeller, Prince Charles, Peter Mandelson, David Cameron and Queen Beatrix of Holland but the list of attendees is different every year.

The cloak of secrecy surrounding the meetings, which ban journalists from attending, has fuelled conspiracy theories that so-called Bilderbergers are planning global domination and world unification.

However, the event is most often likened to a political version of the World Economic Forum in Davos, Switzerland, which draws members of high society to discuss business and the economy.

Its steering commitee includes Mr Clarke, Cabinet minister without portfolio, Thomas Enders, chief executive of defence company EADS, and Peter Sutherland, the chairman of Goldman Sachs.

Some activists have decided to hold a Bilderberg Fringe Festival – described by its organisers as a peaceful weekend of speakers, comedy, music, workshops, arts and entertainment nearby. However, Dorothy Thornhill, the mayor of Watford, has raised fears that the summit could also bring “violence.”

She told the Watford Observer: “I have my concerns about it because it does attract people who can and do cause violence and disturbance.

“But I am confident the police will be able to minimise that and give them their right to protest.

“I am ambivalent about whether this is a good thing. It’s potentially a positive thing as long as things don’t kick off.

Hertfordshire Police said the Bilderberg Group has agreed to contribute some of the cost of security, but taxpayers will have to cover the rest of the bill.

The force said it could not yet estimate the cost to the taxpayer of policing the event or whether it will need to draw on reinforcements from nearby forces.

“The organisers of the event are paying for a private security firm who will be providing security at the venue,” the spokesman said.

“In addition, the organisers have agreed to contribute towards policing costs relating to the event.

“As we do not disclose the costs of operations prior to their event, we will not disclose the amounts at this stage.”

The last time the Bilderberg Group met in Britain was in Turnberry in Scotland in 1998. This year’s event will be at the Grove Hotel in Watford, which has been booked out for the duration of the conference from 6th to 9th June.